Numerous types of mixers are known in the prior art which provide for the mixing of liquids in large vessels on a commercial scale to carry out industrial and commercial processes on a substantially continuous, non-batch, basis. Two important examples of such continuous processes are froth separation and solvent extraction electrowinning, both of which processes are widely employed in the field of mining for the cost effective separation of minerals from their ores. While the mixers used in these and other substantially continuous industrial or commercial processes have traditionally been of the well-known electrically driven propeller type, recent concerns have surfaced over the energy consumption of such propeller mixers, and as to the actual mixing efficiency achieved thereby in large vessels. This latter concern should be readily apparent to those skilled in the art from an observation of the relative localized perturbation (and hence mixing) that is apparent around the perimeter of vessels having a relatively large diameter as compared to the diameter of the mixing head of the propeller mixer, and from a realization that the angular velocity (and hence shear forces) vary greatly as one moves radially outwardly from the centre of the mixing head of a propeller mixer towards it tip. As a result, an increasing need exists in the prior art for commercial scale process mixers which are more efficient than the conventional propeller type mixers conventionally used in such processes.
Accordingly, there has existed for a considerable period of time a longstanding need for more efficient mixing devices suitable for use in the mixing of liquids in large vessels on a commercial scale for carrying out industrial and commercial processes on a substantially continuous, non-batch, basis. One solution in this regard has been provided in the form of a non-propeller type mixer as shown in International Application Number PCT/CA02/00528 published on Oct. 24, 2002 under publication number WO 02/083280 A1, which application has as one of its co-inventors Mr. Gary Haughton, a co-inventor also named in the present application.
The Haughton PCT/CA02/00528 invention relates, inter alia, to a non-propeller type mixing apparatus for use with a vessel substantially centered about a longitudinal axis. The mixer has a generally circular (in plan outline) blade which has a central head axis, a first end and a second end spaced from the first end along the head axis. The blade preferably tapers in a frusto-conical manner from the first end to the second end. The mixing blade is mounted within the vessel for reciprocating longitudinal motion with the central head axis substantially coaxial to the longitudinal axis of the vessel, and means are provided for imparting said reciprocating longitudinal movement to the mixing head, said means preferably comprising a scotch yoke mechanism. The scotch yoke mechanism is operatively connected to the blade by a drive shaft, and the scotch yoke mechanism effects said reciprocating longitudinal movement of the blade in a controlled manner with particularly advantageous operating parameters for efficient mixing being disclosed in the subject application.
The present invention relates to improvements to non-propeller type mixers of the general type disclosed in PCT Patent Application Number PCT/CA02/00528. More particularly, and without limitation, such improvements include: improvements to the mixer which facilitate the quick installation and removal of the scotch yoke mechanism from atop the mixing vessel (for repair or replacement) whilst maintaining the central head axis substantially coaxial to the longitudinal axis of the vessel; improvements to the configuration of the mixing blade; improvements to the scotch yoke mechanism which facilitate its installation, service life, operation, reliability, and ease of service; and improvements which particularly adapt the mixer disclosed for use with closed vessels containing explosive or otherwise dangerous gases, such as sewage digesters, wherein the escape of such dangerous gases from the closed vessel must be minimized at all times.
There is thus disclosed according to one aspect of the present invention a mixing apparatus for use with a vessel having a contiguous sidewall substantially centered about and defining a longitudinal axis, the mixing apparatus having a base plate removably mountable atop the vessel, a table frame removably mountable atop the base plate and a housing removably mountable atop the table frame. The apparatus also features a mixing head comprising a generally annular blade body for immersion into the fluids to be mixed within the vessel, the blade body having a centrally positioned hub member defining a substantially vertically directed hub axis, said hub member being attached to and surrounded by a ring portion defining an orifice having a centre of symmetry. A drive shaft is provided for supporting the mixing head within the vessel and extending from the hub member to the housing. A reciprocating drive assembly is mounted substantially within the housing, the reciprocating drive assembly being operatively connectable to the drive shaft for imparting reciprocating longitudinal movement to the mixing head. A linear bearing assembly is mounted on the table frame in proximal relation to the housing, with the drive shaft operatively slidable within the linear bearing assembly. With this arrangement, the mixing apparatus is positioned atop the vessel with the drive shaft, hub axis and centre of symmetry all being substantially aligned with said longitudinal axis.
According to another aspect of the invention, the mixing apparatus is constructed with the housing having a housing base plate adjacent its lower end, the table frame having a top plate adjacent its upper end, and with the housing being mountable atop the top plate in removable contacting relation therewith. The housing also preferably has a removable front cover plate with the linear bearing assembly operably mountable on the top plate with its upper end protruding thereabove into the interior of the housing. The housing is constructed and otherwise adapted to be laterally slidable to remove the upper end of the linear bearing from within the interior of the housing when the front cover plate of the housing is removed and the drive shaft is operatively disconnected from the reciprocating drive assembly. Such lateral sliding of the housing is accommodated by means of an open-ended notch formed along a front edge of the housing base plate, with the open-ended notch being shaped and dimensioned to surroundingly receive the upper end of the linear bearing within the arms of said notch. Such lateral sliding of the housing simplifies assembly, disassembly and servicing of the mixing apparatus. It further allows for removal of the entire housing and drive components therein (i.e. the scotch yoke mechanism) for easy repair or quick replacement, thereby minimizing potential down time (and the associated significant economic loss) for the mixing vessel, which as indicated above, is typically utilized in large scale continuous processing systems.
According to yet a further aspect of the invention, the above mixing apparatus further comprises a screw jack assembly operatively interconnected between the housing and the table frame for mechanically assisting with the aforementioned lateral sliding of the housing.
According to yet a further aspect of the subject invention, the table frame preferably has a plurality of table legs and is removably mountable atop the base plate by means of said table legs. This feature also simplifies assembly, disassembly and servicing of the mixing apparatus and its associated components and sub-assemblies and allows the more service intensive components of the device (e.g. the reciprocating drive assembly) to be at a convenient height for access by service personnel without significant stooping or bending and consequential discomfort, distress or back injury.
According to a particularly advantageous aspect of the invention, the drive shaft is comprised of at least two sections being releasably interconnectable one to the other, being an upper drive shaft section and a lower drive shaft section, wherein the upper drive shaft section is dimensioned and otherwise adapted to extend from its operative connection with the reciprocating drive assembly through the linear bearing to a point of releasable interconnection with the lower drive shaft section, which point is, at all times of operation of the mixing apparatus, located above the base plate. The lower drive shaft section extends from the point of releasable interconnection with the upper drive shaft section through an aperture in the base plate to terminate at a point of connection with the hub member. A raised annular flange member is preferably mounted on the base plate in encircling relation to the aperture, and a lock means is provided for selectively interacting with the lower drive shaft member and the annular flange member to prevent longitudinal sliding of the lower drive shaft section relative to the annular flange member. This arrangement facilitates leaving the lower drive shaft section and the mixing head (attached to its lower end) suspended within the interior of the mixing vessel whilst the entire mixing apparatus thereabove (consisting primarily of the housing, the reciprocating drive components housed therein, and the table frame) can be removed from the top of the vessel, for easy repair or quick replacement without the need for a large lifting crane, as would otherwise be required to lift the entire mixing assembly out of and clear from the top the mixing vessel. Moreover, in applications involving sealed mixing vessels, this arrangement facilitates easy access for servicing to the seals or other components that are installed (as described more fully hereinbelow) adjacent to the base plate below the level of the top plate of the table frame.
According to yet a further aspect of the present invention the aforementioned seal is a substantially annular seal member mounted on the interior of the annular flange member for selective inflation to fill the void between the lower drive shaft section and the interior of the flange for selective sealing of the escape of gas from the interior of the vessel to atmosphere around said upper drive shaft section.
According to still a further aspect of the present invention as adapted for use with sealed vessels, a further gas sealing means is disclosed which comprises, in combination, the use of gas seals within the lower end of the linear bearing positioned in gas sealing relation to the upper drive shaft section, which linear bearing projects downwardly below the top plate of the table frame, an upper annular flange member mounted on the underside of the top plate in gas sealing relation to said top plate and in encircling relation to the lower end of the linear bearing, and a resilient rubber sleeve member extending from the lower annular flange member to the upper annular flange member, with the sleeve member being releasably connectable to both of said annular flanges in gas sealing encircling relation thereto.
Further aspects of the present invention relate to improvements in the design and construction of the scotch yoke type of reciprocating drive assembly preferably used in the subject mixing apparatus, in the manner of delivering lubrication to the key wear components of assembly, and to the design and construction of alternate forms of mixing heads for use as a component of the mixing apparatus.
These and other aspects, advantages, features and characteristics of the present invention, as well as methods of operation and functions of the related elements of the structure, and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings, the latter of which is briefly described hereinbelow.